The present invention relates generally to optical devices and, more particularly, to a method, apparatus and system for aligning an end of an optical fiber with an optical waveguide of an optical waveguide device.
When optical fibers are directly coupled to an input of an optical device in a non-pigtailed configuration, the end of the input optical fiber is secured to an input of an optical waveguide formed in the optical device. Likewise, an end of an output optical fiber is secured to an output of the optical waveguide. The optical fiber ends typically are secured to the input and output of the optical waveguide by adhesive. With these types of optical devices, the ends of the optical fibers are typically directly secured to the inputs and outputs of the optical waveguides.
In the past, alignment of the waveguides of an optical device under test (DUT) was generally performed by injecting light into the input optical fiber secured to the input of the optical waveguide and then measuring the output of the optical fiber secured to the output of the optical waveguide. If the measured output was determined to be correct (i.e., to provide the expected or desirable results), the optical waveguide was deemed to be operating properly. On the other hand, if the measured output did not provide the correct or expected results, the optical waveguide was deemed to be operating improperly. One of the problems associated with this manner of testing is that securing the optical fibers to the waveguide input and output is a waste of time if it is subsequently determined during testing that the waveguide does not function properly.
Currently, alignment systems exist that test the optical device before the ends of the optical fibers are secured to the optical device. Such systems place an end of the input optical fiber in very close proximity to the optical waveguide input, detect the light propagating out of the optical waveguide output, and determine, based on the detected light, whether the optical waveguide is aligned. Once the waveguide is aligned, light propagating out of the output of the optical waveguide can be processed to determine whether the waveguide is operating properly. Thus, the input and output optical fibers are not secured to the inputs and outputs of the optical waveguides of an optical device until after all of the optical waveguides have been tested and a determination has been made that the optical waveguides are operating properly. If a determination is made that one or more optical waveguides are not functioning properly, the optical fibers are not secured to the optical device, and thus no time is wasted securing optical fibers to a defective optical device that will not be shipped to a customer.
The known alignment systems utilize an infrared (IR) camera that is positioned to view the outputs of one or more optical waveguides of the optical device. The IR camera converts the IR signals into electrical signals, which are then processed and displayed on a display device. Based on the displayed information, the optical fiber end is moved with respect to the optical device until it is determined that alignment of the optical fiber end and the input of the optical waveguide has been achieved. As the end of the optical fiber is moved, the output from the IR camera is processed to determine whether alignment has been achieved.
In some of these types of alignment systems, the process of adjusting the position of the optical fiber end until alignment is achieved is performed manually by a human operator who looks at the display device and determines, based on the displayed information, whether alignment has been achieved or whether the position of the fiber end needs to be spatially adjusted. Generally, the operator moves the fiber end until the operator is satisfied that the fiber end is aligned with the optical waveguide. In other alignment systems, the process of moving the end of the optical fiber until alignment is achieved is automated. Some of the disadvantages of the manual alignment approach are that it is prone to human error, subjective, difficult to teach and time consuming to perform.
One of the advantages of the known manual and automated alignment systems is that, because the camera has many optical detector elements (i.e., pixels), the camera sees both spatial resolution as well as light intensity distribution. However, one of the disadvantages of using a camera for this purpose is that it must first be calibrated to the optical fiber before the alignment process can begin. A calibration algorithm must be performed to detect the end of the optical fiber in order to ensure that the camera is viewing the correct object area. Because performing this type of detection is relatively complicated, the calibration algorithm is processing intensive. Once the calibration is complete, then the alignment algorithm can begin being executed.
During the alignment algorithm, at least a thousand pixels per frame must be processed, and many frames must be processed. Processing this much information further increases processing overhead of the computer that executes the alignment algorithm. Furthermore, the frame rate of the IR camera is relatively slow (e.g., about 30 frames per second), which limits the speed at which the alignment information is output to and processed by the computer. All of these factors limit the speed at which the alignment process, both manual and automated, can be performed.
In addition, the costs associated with purchasing the IR camera, developing the calibration and alignment software, and integrating the software with the IR camera is relatively expensive. Accordingly, a need exists for an alignment system that enables precise alignment to be consistently achieved without requiring a large amount of processing overhead. A need also exists for an alignment system that is well suited for automation and that enables the automation process to be performed at relatively high speeds. A further need exists for an alignment system that is relatively inexpensive compared to known alignment systems.
In accordance with the present invention, it has been determined that the output of a single optical sensor can be processed and converted into digital signals, which are then further processed in accordance with an alignment algorithm that generates feedback signals that are sent to a motion control system that is capable of adjusting the spatial positioning of the optical fiber end until alignment between the end of the optical fiber and the input of an optical waveguide of an optical device is achieved. The alignment system includes a single optical sensor, a lens and processing logic. The processing logic includes an electrical processing circuit that generates an amplified, filtered signal with low noise and a wide dynamic range, an analog-to-digital converter (ADC) that converts the output of the electrical processing circuitry into digital signals, and a computer, which processes the digital signals in accordance with the alignment algorithm to generate the feedback signals that enable the end of the optical fiber to be aligned with the input of the optical waveguide.
Once the optical fiber end is aligned with the input of the optical waveguide, the spatially aligned position of the end of the optical fiber is maintained. This enables the optical device to be tested for defects by measuring and analyzing the output of the optical waveguide, although the present invention is usable for other applications. Known motion control systems and motion control algorithms can be utilized in conjunction with the method and apparatus of the present invention to spatially position the end of the optical fiber.
By using a single optical sensor to achieve alignment, as opposed to a camera, the cost of the alignment system is greatly reduced. Furthermore, since the alignment algorithm is only required to deal with the output of a single optical sensor, as opposed to potentially thousands of pixels of an IR camera, the processing overhead associated with performing the alignment algorithm is relatively low. This low processing overhead enables alignment to be achieved relatively quickly using a relatively low cost alignment system.
These and other features and advantages of the present invention will become apparent from the following description, drawings and claims.